It has been demonstrated that bi-domain peptides, which contain a factor XIIIa substrate sequence and a bioactive peptide sequence, can be cross-linked into fibrin gels and furthermore, that this bioactive peptide retains its cellular activity in vitro. While peptides can partially mimic the bioactivity of the whole protein from which they are derived, this bioactivity is usually lower than the bioactivity of the whole protein, and sometimes it is impossible to mimic certain proteins with only a short peptide. In order to incorporate the specific bioactivity of these types of factors, such as growth factors, it would be beneficial for the entire protein to be incorporated into the fibrin matrix.